Osmotic devices for delivering a beneficial medicine to living environments of use are known to the prior art in U.S. Pat. No. 3,845,770, issued to Theeuwes and Higuchi, and in U.S. Pat. No. 3,916,899, issued to the same patentees. The osmotic devices disclosed in these patents comprise a semipermeable wall that surrounds a compartment containing a beneficial medicine. The semipermeable wall is permeable to the passage of an external fluid, and it is substantially impermeable to the passage of medicines. An osmotic passageway is provided through the wall for delivering the beneficial medicine from the device. These prior art devices release the beneficial medicine by imbibing fluid through the semipermeable wall into the compartment, to form in the device an aqueous solution containing the beneficial medicine that is dispensed through the passageway from the device. The external fluid is imbibed through the semipermeable wall into the compartment in a tendency towards osmotic equilibrium, at a rate determined by the permeability of the semipermeable wall and the osmotic pressure gradient across the wall. These devices are extraordinarily effective for delivering a medicament that is soluble in the fluid and exhibit an osmotic pressure gradient across the semipermeable wall against the external fluid, and for delivering a medicament that has limited solubility in the fluid and is admixed with an osmotically effective osmagent that is soluble in the fluid and exhibits an osmotic pressure gradient across the semipermeable wall against the fluid. The beneficial medicament is incorporated into these devices during manufacture, prior to forming the semipermeable wall around the compartment. These prior art osmotic devices generally contained a large amount of medicine, and they operated successfully for delivering the medicine to the environment of use.
Prior to this invention a critical need existed in the pharmaceutical dispensing art for an osmotic device that contained a small amount of medicine and successfully dispensed the medicine to the environment of use. The need existed for an osmotic device that both contained and dispensed small amounts of medicine because many medicines are therapeutically effective in small amounts. The need existed also for an osmotic device that housed smaller amounts of medicine because of the difficulty encountered in formulating a compartment containing a small amount of medicine, and because of the difficulties encountered in surrounding a small amount of medicine with a semipermeable wall.